Of those interviewed, 43 percent said they felt negatively about the treatment they had received from police. Thirty-nine percent of them said they had been detained, 31 percent of them had had their vehicles impounded, and 23 percent said they had been reported to immigration authorities, according to the study.

Illegal immigrants have developed various strategies to cope with the fear of living in the shadows, Garcia said. Many of them avoid public places, they avoid contact with law enforcement, and when they need to report a crime, they ask a friend or family member to make the report on their behalf, she said.

According to the survey, 18 of the 202 immigrants surveyed said they had been either a witness to or a victim of a crime. Of those, only three ---- one legal immigrant and two illegal immigrants ---- said they had reported the crime to police, according to the report.

Bill Flores, a retired assistant sheriff and member of the civil rights group El Grupo, said local law enforcement agencies should leave immigration enforcement to federal authorities. Immigrants who believe the agency is working hand in hand with immigration authorities will be less likely to report crimes, he said.

"This association (between local law enforcement and immigration authorities) runs counter to what many local law enforcement agencies already know and that is that these types of associations have a negative impact on local law enforcement's relationship with this segment of the community," Flores said.